Tuesday, February 06, 2007

Gas pressures and tipping points

There’s been a lot of hoopla about the recent IPCC report recently. The main effect of this report is that journalists and politicians now know just how boring climate research actually is, so I’ll talk about more interesting gas-based tipping points.

For example, this afternoon on my ride home from work, I discovered the tipping point created by a gradual decrease in the air pressure of the front tyre of a bicycle. As the gas pressure decreases, the tyre footprint on the ground expands, and this gradually increases the traction- until the tipping point. Past that, the tyre collapses, the grip disappears, and the bicycle ‘flips’ to a new metastable state with lower gravitational potential energy. This is shortly followed by the frictional dissipation of any kinetic energy, which was quite substantial this afternoon.

But the real stinker is that I seem to instinctively land in the same position every time I go down- whether falling off a bike or motorcycle, whether turning left or right, at speeds from ten to eighty kph. So I won’t even get any cool new scars from this stack- I’ve just worn the same old ones off again. Although I did manage to write and worm enough to get red welts all over by right side, so the impact points only bled a little. Still, I might take the bus tomorrow.


James Annan said...

Perhaps too late, but hydrogen peroxide is absolute magic for cleaning road rash.

C W Magee said...

Thanks- I'll remember that for next time. This lot all scabbed up in 24 hours, though. I reckon they only get real nasty when I grind down into that white fatty layer.